Why did these young men age so quickly? Explain.

I assume you are referring to Alfons? If so, Alfons was completely unprepared for his role in the war. His participation in the Hitler Youth did not prepare him for facing the Allies on the front lines, for losing his close friends in battle, or for the reality of the British bombers that flew overhead. He was overwhelmed by the number of young men who were readt to desert, and he was panicked by the knowledge if they did, in fact, desert... he himself would lose his life for their actions.